BT-6 Gas

DispersionImpellerThe unique blade geometry of the BT-6 createsoptimal flow conditions above and below the discto efficiently disperses gas at even the highestflow rate.

Chemineers BT-6 Impeller provides

you with technology in gas dispersionapplications. The BT-6 Impeller isthe result of a cooperative venturebetween the Chemineer, Inc. R&Dgroup and its academic affiliates. Itwas developed using the most modernflow measurement techniques and itspatented blade geometry efficientlydisperses gas at even the highestflow rates.Because the BT-6 has such an efficientdispersion mechanism, this impellercan handle more than five times asmuch gas as the D-6 impeller (Rushtonturbine) before flooding, and more thantwice as much as Chemineers concaveblade CD-6 impeller (Smith turbine).Another benefit is a very flat powerdraw curve under gassed conditions.Since its power draw varies little withgas flow rate, the BT-6 impeller isparticularly well suited for applicationswhere flow rates change during theprocess, such as hydrogenationreactors. Another advantage of themore constant power draw is thatchanges in mass transfer during the

process are smaller than with other

impellers. Additionally, the powerdraw of the BT-6 shows minimalvariation when exposed to changesin liquid viscosity; it remains constantfor Reynolds numbers well belowone thousand, which corresponds toviscosities of several thousandcentipoise in typical industrialapplications.The blade design, asymmetric aboutthe plane of the disc, has beenoptimized to take into account thedifferent flow conditions above andbelow the disc. The BT-6 impellersasymmetric design allows the overhangon the top of the blade to capture therising gas flow. The gas flow is thendispersed from a strong turbulentvortex on the inside of the deep blade.No cavities form on the trailing edgesof the blades.In tall tanks the radial pumping BT-6is used as the primary gas dispersionimpeller mounted directly above thegas sparger in the bottom of the tank.Axial flow impellers, such as the wideblade Maxflo hydrofoil or the narrowblade XE-3 high-efficiency impeller, areused as upper impellers. This impellerconfiguration combines efficient gas

Impeller FeaturesBT-6 impellers are available in thenormal configuration of 6 bladeswith a choice of welded, bolted, orbolted- adjustable blades. Standardmaterials of construction are carbonsteel or 316 stainless. Fabricationsfrom special alloys are also available.Please contact your Chemineer salesrepresentative for assistance with yourspecific gas dispersion requirements.

D-6 (1950s)

CD-6 (1980s)

BT-6 (2000s)

Three Generations of Gas Dispersion Impeller Technology

The BT-6 is the leader in gas dispersion impeller technology.For over thirty years the D-6 (Rushton) disc style turbine with flatblades was the primary choice for gas dispersion applications.In the late 1980s Chemineer developed the CD-6 impellerwhich is characterized by its concave blade shape. The CD-6rapidly established itself as far superior to the D-6 with itscapability of dispersing more gas combined with a power drawconsiderably less sensitive to changes in the gas flow rate. TheCD-6 revolutionized the field of gas-liquid agitation and quicklybecame the standard design. There are more than 200,000HP of agitators installed with this impeller. The next generationgas dispersion impeller, the BT-6, is the result of the knowledgegained from our broad CD-6 installation base and our extensiveresearch and development efforts. The BT-6 technology combinesthe concave blade concept with vertically asymmetric blades thatare shaped to make optimum use of the different flow conditionsBT-6CD-6

above and below the impeller. The photos above show a comparisonbetween the dispersion performance of the three impellers at a veryhigh gas flow rate of 13 VVM, corresponding to a superficial gasvelocity of more than 0.1 m/s (0.33 ft/s) at this scale. At this highgas flow rate, the D-6 (left) is clearly flooded and cannot dispersethe gas. This is apparent from the gas that shrouds the impeller andthe surging surface as large gas bubbles jet through the system.The CD-6 (center) disperses the gas, driving it to the vessel walland producing a smooth surface. The BT-6 (right) not only forcesthe gas to the wall, it distributes the gas throughout the entire liquidvolume, bottom to top, providing better mass transfer and uniformity.The higher liquid level in the vessel indicates a higher gas holdup,one of the reasons for the improved mass transfer. In studies ofdozens of different impeller styles the BT-6 consistently producedthe most uniform gas dispersion. The BT-6, with more than 300,000HP of installed agitator power, is always the right choice for your gasdispersion applications.

Mass Transfer Comparison

The rate of mass transfer between the gas and the liquid is ofcritical importance in many processes. The graph shows a masstransfer comparison between the BT-6, the CD-6 and the D-6. Themass transfer coefficient is plotted as a function of the superficialgas velocity. All impellers are operating at the same speed and aredesigned to draw the same ungassed power. As the gas flow rateincreases so does the mass transfer coefficient. At the highest gasflow rates the CD-6 impeller provides more than 40% improvementin mass transfer over the D-6. The BT-6 increases the mass transferrate by as much as 60% when compared to the D-6.

National Oilwell Varco has produced this brochure for general information only, and it is not intended for design purposes. Although every effort has been made to maintain theaccuracy and reliability of its contents, National Oilwell Varco in no way assumes responsibility or liability for any loss, damage or injury resulting from the use of informationand data herein. All applications for the material described are at the users risk and are the users responsibility. All brands listed are trademarks of National Oilwell Varco. 2013 by Chemineer, Inc.